1. Field of the Invention
The present invention relates to an apparatus for spinning filaments from a polymeric material, and more particularly, to a spinning apparatus that has a multiple-temperature control arrangement therein.
2. Description of the Prior Art
Shown in FIG. 1 is a side elevational view, partly in section, of the main functional elements of a spinning apparatus generally indicated by the reference character 10 for spinning fiber filaments from a molten mass of polymeric material, such as nylon polymer. The spinning apparatus 10 is housed in the internal central chamber 12 defined within a hollow-walled casing 14.
Structurally, the spinning apparatus 10 includes a pump 18 mounted on a pump block 20, also known as a "wear plate". The pump block 20 may be supported within the casing 14 by an abutment 22. Depending from the undersurface of the pump block 20 is one or more spin packs, each generally indicated by the reference character 24. Each spin pack 24 is connected to the pump block 20 by one or more mounting bolts 26. Each spin pack 24 is comprised of a pack lid 28, a polymer filter holder 30, and a spinneret plate 36. The filter holder 30 has a central recess 32 therein. The lid 28 and the recess 32 in the filter holder 30 cooperate to define an enclosed pocket in which a polymer filter medium 34, such as sand, is received. The spinneret plate 36 is a relatively massive member that has an array of small, precision bores 36B extending therethrough. The mouths of the bores 36B form an array of orifices that open across the lower surface of the spinneret plate 36.
The pump block 20 has arranged therein one or more internal channels 20C which cooperate to define separate, polymer flow passages that connect the outlet of the pump 18 to the inlet of each spin pack 24 associated with the block 20. The pack lid 28 in each spin pack has an internal passage 28P that leads from the surface of the lid 28 to the pocket in which the filter medium 34 is received. A plurality of smaller internal feeder ducts 30F are provided through filter holder 30 that connect the outlet of the filter 34 with each of the bores 36B extending through the spinneret plate 36. Rails 38 may be provided to protect the face of the spinneret plate 36, if desired
During the spinning operation molten polymer is supplied to the pump block 20 through a jacketed polymer feed line 40. Polymer is conveyed through a set of channels (not shown) in the block 20 to the inlet of the pump 18. Polymer is conveyed to the inlet of the pump 18 at a predetermined polymer inlet temperature. The pump 18 forces the polymer under increased pressure through each of the separate polymer passages formed by the channels 20C in the block 20 to a respective one of the spin packs 24 associated with the block 20. The internal channels 20C which form each separate polymer passage are arranged within the pump block 20 in a manner which insures that polymer traversing through each polymer flow passage travels a substantially equal linear distance from the outlet of the pump 18 to a spin pack 24.
The polymer conveyed to a given spin pack 24 is carried through the passage 28P in the pack lid 28 to the filter 34. From the filter 34 the polymer flows through the feeder channels 30F and to the bores 36B in the spinneret plate 36. The polymer as pressurized by the pump 18 is extruded through the bores 36B in the spinneret plate 36, and emanates from the orifices in the face of the spinneret plate 36 as fine filaments of polymeric material.
The hollow interiors 14I of the walls of the casing 14 are interconnected to form a common fluid flow volume that surrounds the internal central chamber 12. The temperature in the chamber 12 in which the elements of the spinning apparatus 10 are disposed is maintained at substantially the predetermined polymer inlet temperature by pumping a gaseous heat exchange fluid through a fluid flow loop that includes the interconnected flow volumes defined within the casing 14. Typically the heat exchange fluid sold by Dow Chemical Company as Dow Therm.RTM. is used in the effort to maintain the ambient temperature within the internal chamber 12 of the casing 14 at the desired temperature. In some instances thermal conduction into the pump 18 and the spin pack(s) 24 is enhanced by the use of interengaged wedges 42. The wedges 42 force these elements of the spinning apparatus 10 into intimate contact with the walls of the surrounding casing 14.
FIG. 2 illustrates the thermal experience of the polymeric material forming any given one of the filaments extruded from the face of the spinneret plate 36. The polymer enters the pump 18 at a predetermined polymer inlet temperature T .sub.pump inlet. The action of the pump 18 raises the polymer temperature to a higher level at the pump outlet, T.sub.pump outlet. The polymer is substantially maintained at this temperature as it moves through the separate polymer passages formed by the channels 20C in the pump block 20 to the spin pack 24. As the polymer is forced through the filter medium 34 within each spin pack 24 the shearing and filtering action imparted by the filter medium 34 increases polymer temperature toward a temperature maximum, indicated in FIG. 2 as temperature T .sub.filter outlet. Thereafter, the temperature of the polymer as it moves through each of the feeder channels 30F and through the bores 36B decreases toward the temperature value T .sub.spinneret at the face of the spinneret plate 36.
Although the shape of the thermal experience curve for each polymeric filament is the same, the temperature of a filament emanating from an orifice in one region of the face of the spinneret plate 36 may vary from the temperature of a filament emanating from an orifice in a different region of the face of the spinneret plate. For example, the temperature value T .sub.spinneret 1 of a filament emanating from an orifice adjacent a lateral edge of the spinneret plate may be substantially different from the temperature value T .sub.spinneret 2 of a filament emanating from an orifice lying along the central plane of the spinneret plate 36.
The reason for the temperature variation of filaments emanating from different regions across the face of the spinneret plate 36 can be understood from FIG. 3, which is a stylized pictorial representation of the thermal gradient formed within a spin pack 24 As seen in FIG. 3 the filter 34 serves as a heat source lying centrally within the spin pack 24. The local polymer temperature has risen above the surrounding spin pack temperature, and heat flows out from this. The bottom side of the spin pack is an exposed metallic surface, being the highest region of heat loss from the system. The hot polymer is also moving toward this surface, and heat is convected from the hotter filter to the filter holder and the spinneret by the polymer. Therefore, the center region of the spinneret is warmer than its edges., because there is no polymer carrying heat to the edges and they are further removed from the hotter filter region. Conduction of heat between the spin pack and the surrounding spin block casing also impacts the spinneret edge temperature.
These temperature differences in the metal of the spin pack translate to corresponding differences in the polymer temperature as it moves down through the spinneret plate and emerges as filaments from the spinneret face. As the filter medium 34 ages the temperature differences are exacerbated. These filament temperatures differences lead to non-uniform filament properties, which is seen as deleterious.
In view of the foregoing it is believed advantageous to provide a temperature control arrangement for a spinning apparatus that reduces or eliminates temperature variations within the spin pack, and especially across the filter holder and the spinneret plate.